An arithmetic of g 1 term in Molodensky's BVP is studied by means of wavelet analysis. It is important to proceed such study because of no requiring to do various corrections related with density of the earth.The existance of the strong singular integral g 1 term is proved under Chauchy's principal value meaning,and also the arithmetic is given. The obtained results show that the arithmetic has the properties of high speed and high accuracy.Particularly,the arithmetic can be used to evaluate g 1 term on large scale of range. [